The invention concerns a transfer device in a packaging machine in accordance with the independent claim.
In a packaging machine, the products and the packages, which can be e.g. folding boxes, must pass several stations either individually or as a unit with the product accommodated in the package. In the sense of the application, the term product means each individual product and also a stack of individual products, e.g. blister strips handled as a unit.
Endless chain or conveyor belts are often used as a transport device within the packaging machine, wherein the packages and/or the products are supplied on the upper run. The following discussion is based, by way of example, on the transfer of a blister stack, consisting of several blister strips disposed on top of each other on a product conveyor belt.
The individual blisters are disposed on top of each other in a stacking station to form a blister stack and are then transferred to the product conveyor belt via a transfer device (EP 0 876 278 B1). The transfer device comprises a sliding surface, one end of which accommodates, in a transfer station, the blister stack which is to be transferred. At a separation above the sliding surface, an endless conveyor is provided which circulates in a vertical plane and carries several projecting fingers circulating with the endless conveyor. To displace the blister stack across the sliding surface, a finger can engage behind the blister stack and carry it while moving along the lower run of the endless conveyor. At the end of the sliding surface, the blister stack is pushed onto the product conveyor belt and is disposed, in particular, in a compartment formed thereon, thereby terminating the transfer.
This type of displacement of the blister stack over the sliding surface has various disadvantages. On the one hand, the finger must be positioned very precisely relative to the blister stack to avoid eccentric introduction of the pushing force and thereby jamming or disalignment of the blister stack. Since the width of the blister stacks to be moved by the transfer device varies depending on the size of the respective blister strips, the position of the fingers must always be re-oriented when the product is changed, which is demanding and laborious. Moreover, there is the risk that the blister stacks are released from the finger during sudden stoppage of the transfer device due to their inertial force to continue to slide over the sliding surface through a short stretch, without guidance, wherein they usually lose their predetermined orientation and must be removed from the packaging machine by an operator to guarantee proper operation when the transfer device is restarted.
In CH 410 759, which discloses a means of this type, a stack of products is inserted into a continuous transport channel by means of a multi-component push arm which is mounted to a first circulating endless conveyor. The transport channel is associated with a second circulating endless conveyor which carries transport straps for displacing the product stack along the transport channel after the push arm has pushed the stack into the transport channel. The speed and orientation of the push arm and the transport straps are adjusted such that the product stack is loaded on its rear side by the push arm at the end of the effective transport path of the first endless conveyor of the push arm, while its front side abuts the advancing transport strap such that a momentary state is thereby achieved in which the product stack is received between two elements.
Such a transfer also involves the above-mentioned drawbacks since the product stack is only in contact with the push arm along nearly the entire displacement path.
It is the underlying purpose of the invention to produce a method and a device for transferring a product in a packaging machine which eliminates the above-mentioned disadvantages to transfer the product with high precision.
This object is achieved in accordance with the invention with the device having the characterizing features of the independent claim.
In accordance with the invention, the pushing motion of the product or of the blister stack is achieved in a conventional manner via the pushing element which engages behind the product, which may be one or more adjacent fingers or also a push plate. During its entire displacement, the product is guided between the pushing element and the advancing limiting element, preferably with tight fit. The advancing limiting element which can also be one or more adjacent fingers or a limiting plate, prevents the product from being released from the pushing element during sudden stoppage of the transfer device to continue to slide in an uncontrolled fashion. Moreover, the limiting element prevents, in cooperation with the pushing element, inclined positioning of the product, since the product is precisely positioned between the pushing element and the limiting element. The separation between the pushing element and the limiting element can be selected such that the product is clamped between these elements with slight pretension. However, the separation between the pushing element and the limiting element preferably corresponds exactly to the width of the product such that it is held between the two elements without any tension.
To achieve high efficiency with the transfer device, a new product or a new blister stack should be introduced during times at which the previous product is still being displaced. To be able to receive the provided product quickly and securely between the pushing element and the limiting element, the invention provides that the advancing limiting element is returned to the transfer station, after termination of displacement of the product, by means of its first endless conveyor and, in particular, via its upper run to serve as pushing element for the next product to be displaced, which is already disposed in the transfer station, by abutting the rear side thereof. The pushing element used for the previous product is returned to the transfer station against the product transport direction by means of its second endless conveyor and, in particular, via its lower run and abuts the front side of the provided product at that location such that it serves as a limiting element for same during the displacement process. In this manner, the fingers of the one endless conveyor and the fingers of the other endless conveyor are alternately used as pushing element and as limiting element, respectively.
It has been demonstrated that an eccentric disposition of the pushing element relative to the product, i.e. eccentric introduction of the pushing force, does not disalign the product due to the limiting element, since the torque resulting from such eccentricity is accommodated for by the limiting element in cooperation with the pushing element. In this fashion, demanding centering of the pushing element relative to the product is not required.
When the format is changed, the separation between the pushing element and the limiting element must merely be adjusted to the width of the new product. Towards this end, the pushing element and the limiting element are advantageously mounted to different endless conveyors which can be adjusted relative to each other. The two endless conveyors are preferably driven independently of each other, wherein the drive motions are synchronized during the entire displacement process of the product to maintain the predetermined separation between the pushing element and the limiting element.
The above-mentioned object is achieved in a device having the characterizing features of the independent claim. The limiting element which advances the product is mounted to the second circulating endless conveyor and is driven thereby, wherein the product is guided between the pushing element and the limiting element, preferably with close tolerance. The pushing element and the limiting element are thereby mounted to different endless conveyors, each of which is preferably provided with its own drive device such that, after termination of displacement of a product in the above-mentioned manner, different return motions for the elements can be provided.
The endless conveyors are preferably disposed above the sliding surface and each circulate parallel to another in a vertical plane.
In accordance with the invention, each endless conveyor can be driven in two directions as a result of which, after termination of the displacement process of a product, the advancing limiting element can be returned, in particular via the upper run of its endless conveyor, to the transfer station while the pushing element is returned to the transfer station against the product transport direction, in particular, via the lower run of its endless conveyor. For the next product to be displaced, the elements thereby swap function, i.e. the previous limiting element becomes the pushing element while the previous pushing element assumes the function of the limiting element.
Further details and features of the invention can be extracted from the following description of embodiments with reference to the enclosed drawing.